Magnetoresistive random access memory

1. Field of the Invention

The invention relates to a semiconductor device, and more particularly to a magnetoresistive random access memory (MRAM).

2. Description of the Prior Art

Magnetoresistance (MR) effect has been known as a kind of effect caused by altering the resistance of a material through variation of outside magnetic field. The physical definition of such effect is defined as a variation in resistance obtained by dividing a difference in resistance under no magnetic interference by the original resistance. Currently, MR effect has been successfully utilized in production of hard disks thereby having important commercial values. Moreover, the characterization of utilizing GMR materials to generate different resistance under different magnetized states could also be used to fabricate MRAM devices, which typically has the advantage of keeping stored data even when the device is not connected to an electrical source.

The aforementioned MR effect has also been used in magnetic field sensor areas including but not limited to for example electronic compass components used in global positioning system (GPS) of cellular phones for providing information regarding moving location to users. Currently, various magnetic field sensor technologies such as anisotropic magnetoresistance (AMR) sensors, GMR sensors, magnetic tunneling junction (MTJ) sensors have been widely developed in the market. Nevertheless, most of these products still pose numerous shortcomings such as high chip area, high cost, high power consumption, limited sensibility, and easily affected by temperature variation and how to come up with an improved device to resolve these issues has become an important task in this field.

According to an embodiment of the present invention, a semiconductor device includes a substrate having an array region defined thereon, a ring of magnetic tunneling junction (MTJ) region surrounding the array region, a gap between the array region and the ring of MTJ region, and metal interconnect patterns overlapping part of the ring of MTJ region. Preferably, the ring of MTJ region further includes a first MTJ region and a second MTJ region extending along a first direction and a third MTJ region and a fourth MTJ region extending along a second direction.

According to another aspect of the present invention, a semiconductor device includes: a substrate having an array region defined thereon; a first ring of magnetic tunneling junction (MTJ) region surrounding the array region; a second ring of MTJ region surrounding the first ring of MTJ region; a third ring of MTJ region surrounding the second ring of MTJ region; a first gap between the array region and the first ring of MTJ region; a second gap between the first ring of MTJ region and the second ring of MTJ region; and a third gap between the second ring of MTJ region and the third ring of MTJ region.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

FIG. 1 illustrates a top view of a MRAM device according to an embodiment of the present invention.

FIG. 2 illustrates a cross-section of the MRAM device along the sectional line AA′ of FIG. 1 .

FIG. 3 illustrates a cross-section of the MRAM device along the sectional line BB′ of FIG. 1 .

FIG. 4 illustrates a top view of a MRAM device according to an embodiment of the present invention.

Referring to FIGS. 1-3 , FIG. 1 illustrates a top view of a semiconductor device, or more specifically a MRAM device according to an embodiment of the present invention, FIG. 2 illustrates a cross-section of the MRAM device along the sectional line AA′ of FIG. 1 , and FIG. 3 illustrates a cross-section of the MRAM device along the sectional line BB′ of FIG. 1 . As shown in FIGS. 1-3 , a substrate 12 made of semiconductor material is first provided, in which the semiconductor material could be selected from the group consisting of silicon (Si), germanium (Ge), Si—Ge compounds, silicon carbide (SiC), and gallium arsenide (GaAs). An array region 14 and a periphery region 16 surrounding the array region 14 are defined on the substrate 12 , in which the array region 14 in this embodiment could also be referred to as a MRAM macro region. The array region 14 could further include a MRAM region 18 and a logic region 20 while the periphery region 16 could include at least a ring of MTJ region 22 surrounding the array region 14 .

Viewing from a more detailed perspective, the MRAM unit shown in FIG. 1 also includes a plurality of metal interconnect patterns 24 overlapping part of the MTJ region 22 and a gap 26 disposed between the array region 14 and the ring of MTJ region 22 so that the ring of MTJ region 22 does not contact the array region 14 directly. In this embodiment, the MTJ region 22 surrounding the array region 14 further includes a first MTJ region 28 and a second MTJ region 30 extending along a first direction (such as X-direction) and a third MTJ region 32 and a fourth MTJ region 34 extending along a second direction (such as Y-direction), in which the first MTJ region 28 overlaps the third MTJ region 32 at a first corner 36 , the first MTJ region 28 overlaps the fourth MTJ region 34 at a second corner 38 , the second MTJ region 30 overlaps the third MTJ region 32 at a third corner 40 , and the second MTJ region 30 overlaps the fourth MTJ region 34 at a fourth corner 42 .

In other words, the first MTJ region 28 , the second MTJ region 30 , the third MTJ region 32 , and the fourth MTJ region 34 together constitute a square-shaped or rectangular-shaped ring surrounding the array region 14 and the metal interconnect patterns 24 overlap each of the first MTJ region 28 , the second MTJ region 30 , the third MTJ region 32 , and the fourth MTJ region 34 , including the metal interconnect patterns 44 overlap the first MTJ region 28 , the metal interconnect patterns 46 overlap the second MTJ region 30 , the metal interconnect patterns 48 overlap the third MTJ region 32 , and the metal interconnect patterns 50 overlap the fourth MTJ region 34 .

In this embodiment, each of the metal interconnect patterns 24 includes a square or rectangle and the metal interconnect patterns 24 not only overlap the first MTJ region 28 , the second MTJ region 30 , the third MTJ region 32 , and the fourth MTJ region 34 surrounding the array region 14 but also overlap the four corners including the first corner 36 , the second corner 38 , the third corner 40 , and the fourth corner 42 . It should be noted that despite only three metal interconnect patterns 24 are shown to overlap each of the first MTJ region 28 , the second MTJ region 30 , the third MTJ region 32 , and the fourth MTJ region 34 , according to an embodiment of the present invention, it would also be desirable to adjust the number of the metal interconnect patterns 24 overlapping the MTJ regions 28 , 30 , 32 , 34 . For instance, it would be desirable to dispose only one or more than one metal interconnect patterns 24 on each of the first MTJ region 28 , the second MTJ region 30 , the third MTJ region 32 , and the fourth MTJ region 34 , which are all within the scope of the present invention.

Moreover, it should be noted that even though each of the metal interconnect patterns 24 in this embodiment preferably share equal size such as equal lengths and equal widths, according to an embodiment of the present invention, it would also be desirable to adjust the sizes of the metal interconnect patterns 24 so that the metal interconnect patterns 24 could have different lengths and/or different widths. For instance, the metal interconnect patterns 24 overlapping the four corners could include a first size and the metal interconnect patters 44 , 46 , 48 , 50 overlapping the first MTJ region 28 , the second MTJ region 30 , the third MTJ region 32 , and the fourth MTJ region 34 could include a second size that is different from the first size, in which the definition of different size in this embodiment could refer to same lengths and different widths or same widths and different lengths, which are all within the scope of the present invention.

According to yet another embodiment of the present invention, the metal interconnect patterns 24 could also be disposed to only overlap the first MTJ region 28 , the second MTJ region 30 , the third MTJ region 32 , and the fourth MTJ region 34 enclosing the array region 14 but not overlapping the four corners including the first corner 36 , the second corner 38 , the third corner 40 , and the fourth corner 42 , which is also within the scope of the present invention.

As shown in the cross-section views in FIGS. 2-3 , active devices such as metal-oxide semiconductor (MOS) transistors, passive devices, conductive layers, and interlayer dielectric (ILD) layer 52 could also be formed on top of the substrate 12 . More specifically, planar MOS transistors or non-planar (such as FinFETs) MOS transistors could be formed on the substrate 12 , in which the MOS transistors could include transistor elements such as gate structures (for example metal gates) and source/drain region, spacers, epitaxial layers, and contact etch stop layer (CESL). The ILD layer 52 could be formed on the substrate 12 to cover the MOS transistors, and a plurality of contact plugs (not shown) could be formed in the ILD layer 52 to electrically connect to the gate structure and/or source/drain region of MOS transistors. Since the fabrication of planar or non-planar transistors and ILD layer is well known to those skilled in the art, the details of which are not explained herein for the sake of brevity.

The semiconductor device also includes metal interconnect structures 54 , 56 disposed on the ILD layer 52 , MTJs 58 disposed on metal interconnect structure 56 on the periphery region 16 and the MRAM region 18 , metal interconnection 60 disposed on the metal interconnect structure 56 on the logic region 20 , cap layer 62 disposed on sidewalls of the MTJs 58 , inter-metal dielectric (IMD) layer 64 disposed around the cap layer 62 , and another metal interconnect structure 66 disposed on the MTJs 58 and the metal interconnection 60 .

In this embodiment, the metal interconnect structure 54 includes a stop layer 68 , an IMD layer 70 , and a plurality of metal interconnections 72 embedded within the stop layer 68 and the IMD layer 70 , the metal interconnect structure 56 includes a stop layer 74 , an IMD layer 76 , and a plurality of metal interconnections 78 embedded in the stop layer 74 and the IMD layer 76 , and the metal interconnect structure 66 includes a stop layer 80 , an IMD layer 82 , and metal interconnections 84 embedded in the stop layer 80 and the IMD layer 82 .

In this embodiment, each of the metal interconnections 72 , 78 , 84 within the metal interconnect structures 54 , 56 , 66 and the metal interconnection 60 could be fabricated according to a single damascene or dual damascene process. For instance, each of the metal interconnections 72 preferably include a trench conductor, each of the metal interconnections 78 preferably include a via conductor, each of the metal interconnections 84 preferably include a via conductor, and the metal interconnection 60 preferably includes a trench conductor.

Moreover, each of the metal interconnections 72 , 78 , 84 could further includes a barrier layer 86 and a metal layer 88 , in which the barrier layer 86 could be selected from the group consisting of titanium (Ti), titanium nitride (TiN), tantalum (Ta), and tantalum nitride (TaN) and the metal layer 88 could be selected from the group consisting of tungsten (W), copper (Cu), aluminum (Al), titanium aluminide (TiAl), and cobalt tungsten phosphide (CoWP). Since single damascene process and dual damascene process are well known to those skilled in the art, the details of which are not explained herein for the sake of brevity. In this embodiment, the metal layers 88 are preferably made of copper, the IMD layers 70 , 76 , 82 are preferably made of silicon oxide, and the stop layers 68 , 74 , 80 are preferably made of nitrogen doped carbide (NDC), silicon nitride, silicon carbon nitride (SiCN), or combination thereof.

In this embodiment, the formation of the MTJs 58 could be accomplished by sequentially forming a first electrode layer 90 , a fixed layer 92 , a free layer 94 , a capping layer 96 , and a second electrode layer 98 on the IMD layer 76 . In this embodiment, the first electrode layer 90 and the second electrode layer 98 are preferably made of conductive material including but not limited to for example Ta, Pt, Cu, Au, Al, or combination thereof. The fixed layer 92 could be made of antiferromagnetic (AFM) material including but not limited to for example ferromanganese (FeMn), platinum manganese (PtMn), iridium manganese (IrMn), nickel oxide (NiO), or combination thereof, in which the fixed layer 92 is formed to fix or limit the direction of magnetic moment of adjacent layers. The free layer 94 could be made of ferromagnetic material including but not limited to for example iron, cobalt, nickel, or alloys thereof such as cobalt-iron-boron (CoFeB), in which the magnetized direction of the free layer 94 could be altered freely depending on the influence of outside magnetic field. The capping layer 96 could be made of insulating material including but not limited to for example oxides such as aluminum oxide (AlO x ) or magnesium oxide (MgO).

Next, a pattern transfer or photo-etching process is conducted by using a patterned resist (not shown) as mask to remove part of the second electrode layer 98 , part of the capping layer 96 , part of the free layer 94 , part of the fixed layer 92 , and part of the first electrode layer 90 to form MTJs 58 on the periphery region 16 and the MRAM region 18 , in which each of the MTJs 58 electrically connect or more specifically directly contact the metal interconnections 78 underneath.

It should be noted that even though the bottom surfaces of the MTJs 58 on the periphery region 16 and the MRAM region 18 all contact the metal interconnections 78 directly, only the MTJs 58 on the MRAM region 18 would connect to active devices such as MOS transistors disposed on the surface of the substrate 12 . In other words, the metal interconnection 78 or metal interconnection 72 connected to the MTJ 58 on the MRAM region 18 are further connected to MOS transistors on the surface of the substrate 12 while the metal interconnections 72 , 78 connected to the MTJ 58 on the periphery region 16 function as dummy metal interconnections are not connected to other wires or metal interconnections underneath.

It should further be noted that the metal interconnections such as the metal interconnection 78 and/or metal interconnection 72 are in fact the metal interconnect patterns 24 overlapping the MTJ region 22 shown in FIG. 1 and the MTJ 58 disposed on the periphery region 16 shown in FIG. 3 if viewed from the top would share same shape as the MTJ region 22 . In other words, the MTJ 58 on the periphery region 16 if viewed from the top would appear as a circular ring or rectangular ring surrounding the entire array region 14 . In contrast to the MTJ 58 on the periphery region 16 surrounding the entire array region 14 in a circular ring or rectangular ring, the MTJ 58 on the MRAM region 18 if viewed from the top would include a shape different from the MTJ 58 on the periphery region 16 . Specifically, the MTJ 58 or MTJs 58 on the MRAM region 18 could appear as individual MTJs arranged according to an array while each of the independent MTJs 58 on the MRAM region 18 could include but not limited to for example a rectangle.

Referring to FIG. 4 , FIG. 4 illustrates a top view of a MRAM device according to an embodiment of the present invention. As shown in FIG. 4 , a substrate 12 made of semiconductor material is first provided, in which the semiconductor material could be selected from the group consisting of silicon (Si), germanium (Ge), Si—Ge compounds, silicon carbide (SiC), and gallium arsenide (GaAs). An array region 14 and a periphery region 16 surrounding the array region 14 are defined on the substrate 12 . Similar to the aforementioned embodiment, the array region 14 in this embodiment could also be referred to as a MRAM macro region and the array region 14 could further include a MRAM region and a logic region while the periphery region 16 could include MTJ regions surrounding the array region 14 .

In contrast to the aforementioned embodiment of only placing a ring of MTJ region around the array region 14 , at least three rings of MTJ regions are disposed around the array region 14 . Preferably, a first ring of MTJ region 102 is disposed around the array region 14 , a second ring of MTJ region 104 is disposed around the first ring of MTJ region 102 , and a third ring of MTJ region 106 is disposed around the second ring of MTJ region 104 , in which gaps are formed between the MTJ regions 102 , 104 , 106 and the array region 14 so that the regions do not contact each other directly. For instance, a first gap 108 is disposed between the array region 14 and the first ring of MTJ region 102 , a second gap 110 is disposed between the first ring of MTJ region 102 and the second ring of MTJ region 104 , and a third gap 112 is disposed between the second ring of MTJ region 104 and the third ring of MTJ region 106 .

In this embodiment, the distance between the array region 14 and the MTJ region 102 is preferably different from the distance between the MTJ regions 102 , 104 , 106 . For instance, the distance S 1 (also referred to as the width of the first gap 108 ) between the array region 14 and the first ring of MTJ region 102 is preferably less than the distance S 2 (also referred to as the width of the second gap 110 ) between the first ring of MTJ region 102 and the second ring of MTJ region 104 , and the distance S 2 between the first ring of MTJ region 102 and the second ring of MTJ region 104 is also less than the distance S 3 (also referred to as the width of the third gap 112 ) between the second ring of MTJ region 104 and the third ring of MTJ region 106 .

Similar to the aforementioned embodiment, the MRAM unit shown in FIG. 4 also includes multiple metal interconnect patterns 24 overlapping part of the MTJ regions 102 , 104 , 106 , in which each of the metal interconnect patterns 24 preferably include a square or rectangle, and the metal interconnect patterns 24 not only overlap the MTJ regions 102 , 104 , 106 surrounding the array region 14 but could also choose to overlap or not overlap the four corners, which are all within the scope of the present invention.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.